Jamming with PLA...not in a musical way

I have a problem that I haven't been able to sort out for weeks. I cannot print PLA. Other materials seem to print fine. The machine is a Taz 4 with an e3d hotend. It's been running flawlessly for over a year now. I cannot for the life of me figure out what has changed. I have:


Tried temperatures from 185-205
Replaced thermistor
Replaced heater, included thermal paste this time
Tried 2 different nozzles, one brand new
Adjusted the nozzle spacing relative to the heat block
Replaced the fan cooling the hot end
Made a new mount for the layer cooling fan so it can be adjusted to not hit the heater block at all
Tried multiple different spools that have printed fine before
Completely disassembled the hotend and cleaned everything thoroughly
The ambient temperature hasn't changed
The humidity is still in a normal range
Tried different print files and tried changing setting and re-slicing


The result is that the printer will print fine for about a centimeter and then jams and strips the filament. I made it as far as 2cm once. ABS prints just fine. PETT prints fine. I feel like this has to be a temperature issue but the hotend is getting the same cooling, if not better, than it was before replacing the heat sink fan.


Any ideas?

I had a problem with PLA jamming. What was happening was I had a small gap between my Wade's extruder and the very top of the nozzle that was plugged into it. If the PLA got too warm it would soften and as the extruder pushed on the PLA it would increase in thickness. At some point, it didn't fit and would jam.

You could try a quick experiment and see if this is happening. Assumming the nozzle is not jammed, bring the heat up to 210 C or 215 C. Way hotter than you would normally print. And just turn the extruder by hand and make sure it feeds with no problem. It might make sense to feed 10 or 15 cm of filament just to verify it feeds ok so long as the plastic going in is cool.

Then let it sit with the heat turned on for a few minutes and just feed 1 cm of plastic into it. Turn off the extruder's heat and let it cool. After cooling off, turn on the extruder's heat long enough that you can retract the filament. When I did this, I could see the filament had buldged about 2 1/2" from the end and that was causing the jam.

So the gap was inside the heat block between the nozzle and the heat break?